East TN Flyer

[East TN Flyer 0]

Has anybody here used a Rotax Triple in their aircraft ?

[Logtrucker 44]

OK, I’ll bite!       Tripple?

[East TN Flyer 0]

Yes, 3 cylinder 2 stroke engines. Mod 779 etc. Commonly used in snow mobiles. Powerful stuff, up to around 150 hp.

[Logtrucker 44]

Thanks ETF, I’m not into snowmobiles anymore at 86, but still have my 1966 skidoo. Had enough playing in the snow hauling logs in the winter! Sounds interesting, haven’t seen them discussed on here but I’m betting someone has checked them out.

[1avidflyer 1983]

Not many Rotax snowmobile engines have the extra metal and machining on the crankcase to hang a gear box on.  That of course limits the options for reduction drives to just a belt drive system.  JImChuk

[East TN Flyer 0]

JimChuck, thanks.

I know a gear drive should be more desireable than a belt drive, but in this case, what would be wrong with a belt drive ? They have been used for many years and are still in use. Anything in particular that you know about ?  Or anybody else ?  Would it be a maintenance issue or weight or reliablility etc ?

Any input will be much appreciated.

[1avidflyer 1983]

Never used belt drive after my Quicksilver MX.  Biggest problem, would be how do you mount it on the engine.  Challengers used a belt drive, but they also used a provision 8 crankcase that the belt drive was mounted on.  (same place as a gear box would have bolted on)  There are belt drives on some Subaru engines, but some of them weigh up to 38 lbs I've heard, and that is twice what a C gear box weighs.  JImChuk

[Allen Sutphin 705]

I flew my challenger with the belt drive for 6 years and it was great on a challenger. Had considered installing it on my fox since I had the engine/belt drive already. I studied it for a while and didn't see anyway that it would work without a lot of work. The gearbox is much easier to install. A belt drive is smoother, less vibration and easier on the prop and engine, but it can have its issues also. V belts require tension to work which is hard on the main bearing. A cog belt doesn't require much tension but if, due to neglect, strips its cogs, you have about 1 minute till things get quiet. A expensive 1 minute. A gearbox has a lot of chatter at low RPM, but also acts as a flywheel somewhat whereas a cog belt absorbs the tortsional  kickback better. If you are willing and able to do the modifications to make it work, its great, but you'd be doing a one-off installation. I just did the one-off thing on installing the Hirth 3202 in the Fox and its a lot of head scratching and redoing things. I have a bigger scrap pile than whats installed on the firewall.

[109jb 181]

If I were going to use a 2-stroke off of a sled other that a provision 8 Ski-Doo, I would be looking at an Arctic Cat 800 fuelie.  There is always a way to mount a gearbox on any motor. I have a 2013 AC 800 High country and the engine is very powerful and with the fuel injection it automatically compensates for altitude, temperature, etc.  It has dual plug heads too.

[Good old number 29 158]

Triples were popular in the late ‘90’s, early 2000’s, but fell out of favor because they are heavier and have less torque than an equal displacement twin. They run smoother, but there are more parts to break. The twin is lighter and more compact, with bigger pistons and a longer stroke. In two stroke engines up to one liter, I’d go for a twin.